1. Field of the Invention:
The present invention relates to a photosensitive member comprising an overcoat layer on a photosensitive layer of organic materials.
2. Description of the Prior Art:
Remarkable progress has been made in the application of electrophotographic techniques since the invention of the Carlson process. Various materials have also been developed for use in electrophotographic photosensitive members.
Organic materials used for the construction of electrophotographic photosensitive members are well known to those skilled in the art (for example, the materials disclosed in the Dec. 15, 1986 issue of Nikkei New Materials, pages 83-98), and these materials have made superior photosensitive members practical from the standpoints of sensitivity, chargeability and construction costs.
Materials used in the construction of organic photosensitive members are, in general, photoconductive materials which produce an electric charge such as, for example, phthalocyanine series pigments, azo series pigments, perillene series pigments and the like, electrical charge transporting materials such as, for example, triphenylmethanes, triphenylamines, hydrazones, styryl compounds, pyrazolines, oxazoles, oxydiazoles, and the like, binding materials for dispersion coating such as, for example, polyester, polyvinyl butyral, polycarbonate, polyarylate, phenoxy, styrene-acryl, and other resins.
Repeated use of these types of photosensitive members, however, gives rise to problems of image defects, white streaks, and the like. These problems arise because the surface hardness of the organic photosensitive member roughly falls within the range from the 5B to B levels of the JIS standards for pencil lead hardness, thus the surface of the photosensitive member is readily damaged due to the friction which is generated when the member comes into contact with the transfer paper, cleaning components, developer, and the like. Another cause of such problems is the harsh surface contact made when paper jams occur and the resultant reversion to manual operation required to remedy the malfunction. Furthermore, damage to the surface of the photosensitive member results in a marked reduction in the surface potential of the member.
In order to eliminate these disadvantages, it is proposed that the surface of the photosensitive member be covered with a protective layer.
The technology described in U.S. Pat. No. 3,956,525 discloses a photosensitive member of the polyvinylcarbazole-selenium type coated with a polymer film having a thickness of 0.1 to 1 microns and formed by glow discharge polymerization as a protective layer.
The technology described in Unexamined Japanese Patent Publication SHO No. 60-61761 discloses a photosensitive member comprising a photactive layer covered by a diamond carbon layer.
The technology described in U.S. Pat. No. 4,544,617 discloses a photosensitive member comprising an amorphous silicon carrier generation and transport layer, trapping layer doped with boron or phosphorous, and an overcoating layer comprised of silicon nitride, silicon carbide or amorphous carbon.
Although the aforementioned manufacturing process disclosed in U.S. Pat. No. 3,956,525 improves the solvent resistance of the photosensitive member, moisture and friction resistances are inadequate, which gives rise to the disadvantages of image drift and cutting. Furthermore, there is no suggestion in the disclosure concerning the improvement of the disadvantages.
The photosensitive member disclosed in Unexamined Japanese Patent Publication SHO No. 60-61761 also has the disadvantages of poor moisture resistance and readily producing image drift.
On the other hand, most organic photosensitive members are poor in terms of heat resistance, that is to say, photosensitivity is reduced when such a member is subjected to a excessive high-temperature heating during the process for providing a protective overcoat layer. The technology disclosed in the aforementioned Unexamined Japanese Patent Publication SHO No. 60-61761 suggests a process for the manufacture of a photoactive layer wherein a diamond carbon layer is successively formed on an amorphous silicon layer normally manufactured at 150.degree. to 300.degree. C. When this process is used on an organic photosensitive member, however, it presents the disadvantage in that the photosensitivity of said member is completely lost.
The photosensitive member disclosed in the aforesaid U.S. Pat. No. 4,544,617 also has poor moisture resistance which has the disadvantage of leading to the production of image drift. This process cannot be applied to the organic photosensitive members because the substrate is subjected to high temperatures during the overcoat layer formation process.
An organic photosensitive member has a relatively soft and easily damaged surface and does not possess an overcoating protective layer which is effective in preventing the production of image drift during long-term use.